Circular stapling instrument

ABSTRACT

A circular stapling instrument including a stapling forming assembly that is actuated independently from actuation of the cutting assembly is provided. The instrument includes a handle assembly, an elongate body extending from the handle assembly, a cartridge assembly mounted on a distal end of the elongate body. The cartridge assembly includes a pusher assembly and a knife assembly. The knife assembly is selectively fixed relative to the pusher assembly.

BACKGROUND

1. Technical Field

The present disclosure relates to circular stapling instruments. Moreparticularly, the present disclosure relates to a circular staplinginstrument having independent strokes for forming staples and cuttingtissue.

2. Background of Related Art

Circular staplers are known, as are their use in closed procedures,i.e., endoscopic, laparoscopic or through natural body orifices.Typically the circular staplers include a tool assembly on a distal endof an elongate body. The tool assembly includes a mechanism for formingstaples and a knife for cutting the stapled tissue. Actuation of thetool assembly may be performed by a manually operated trigger or apowered drive assembly. Generally, both the actuation of the stapleforming mechanism and the advancement of the knife occur at the sametime, i.e., simultaneously. Thus, the force provided by the actuationassembly must be sufficient to overcome the force required to form thestaples and the force required to advance the knife through the tissuebeing stapled. Further, the simultaneous actuation of the staple formingmechanism and advancement of the knife requires that the staple formingmechanism and the knife travel the same distance, thereby limiting thestaple formation height to the knife travel distance.

Therefore, it would be beneficial to have a circular stapler including atool assembly configured to form staples independently of cuttingtissue.

SUMMARY

Accordingly, a circular stapler including a stapling forming assemblythat is actuated independently from actuation of the cutting assembly isprovided. The circular stapler including, a handle assembly, an elongatebody extending from the handle assembly, and a cartridge assemblymounted on a distal end of the elongate body. The cartridge assemblyincludes a pusher assembly and a knife assembly. The knife assembly isselectively fixed relative to the pusher assembly for independentmovement relative to the pusher assembly. The knife assembly isinitially detached from the pusher assembly in a first stroke andsubsequently attached to the pusher assembly in a second stroke.

In one embodiment, the pusher assembly includes a pusher adapterconfigured to be advanced a first distance and retracted a seconddistance, the second distance being greater than the first distance. Theknife assembly may support a snap ring therearound and the pusheradapter includes a ridge formed about an inner surface thereofconfigured to engage the snap ring of the knife assembly.

In some embodiments, the knife assembly includes a knife carrier, aknife supported on and extending distally from the knife carrier and asnap ring supported around a proximal portion of knife carrier. Theknife carrier may include an annular groove configured to accommodatethe snap ring when the snap ring is in a radially compressed conditionand when the snap ring is in an uncompressed condition. The snap ringmay not extend beyond an outer diameter of the knife carrier when thesnap ring is in the compressed condition. The snap ring may extendbeyond an outer diameter of the knife carrier when the snap ring is inthe uncompressed condition. The knife carrier may further include a stepformed in the annular groove configured to engage the snap ring when thesnap ring is in the uncompressed condition. The step may be configuredto prevent radial compression of the snap ring during a tissue cuttingstroke. The cartridge assembly may include a housing having an outercylindrical portion and an inner cylindrical portion, wherein the pusherassembly and knife assembly are substantially cylindrical and areselectively received between the inner and outer cylindrical portions ofthe housing.

Also provided is a method of stapling tissue, including the steps ofproviding a surgical stapling instrument having a pusher and a knifeassembly, wherein the knife assembly is selectively connected relativeto the pusher assembly for independent movement relative to the pusherassembly, advancing the pusher assembly to cause an ejection and aforming of staples, retracting a pusher adapter of the pusher assembly,and advancing the pusher adapter to cause an advancement of the knifeassembly and a cutting of tissue. The method may further include thestep of providing a lapse of time between the ejection and forming ofthe staples and the cutting of tissue to allow for tissue normalization.The step of retracting the pusher adapter may include retracting thepusher adapter to a location proximal of an initial location of thepusher adapter.

DESCRIPTION OF THE DRAWINGS

Embodiments of a surgical stapling instrument including a cartridgeassembly that is actuated independently from actuation of the cuttingassembly are disclosed herein with reference to the drawings, wherein:

FIG. 1 is a perspective view of a surgical stapling instrument includinga cartridge assembly according to an embodiment of the presentdisclosure;

FIG. 2 is an enlarged perspective view of the cartridge assembly of thesurgical stapling instrument of FIG. 1;

FIG. 3 is an exploded perspective view of the cartridge assembly of FIG.2;

FIG. 4 is a perspective view of a knife assembly of the cartridgeassembly of FIG. 2;

FIG. 5 is an exploded view of the knife assembly of FIG. 4;

FIG. 6 is an enlarged view of the indicated portion of FIG. 5;

FIG. 7 is a cross-section side view of the knife assembly of FIG. 4;

FIG. 8 is a cross-sectional side view of the cartridge assembly of FIG.2, in a first or initial position;

FIG. 9 is a cross-sectional side view of the cartridge assembly of FIG.2, after the completion of the first or staple forming stroke;

FIG. 10 is a cross-sectional side view of the cartridge assembly of FIG.2, in a retracted position following the first or staple forming stroke;

FIG. 11 is a cross-sectional side view of the cartridge assembly of FIG.2, during a second or tissue cutting stroke; and

FIG. 12 is a cross-sectional side view of the cartridge assembly of FIG.2, after the completion of the second or tissue cutting stroke.

DETAILED DESCRIPTION

An embodiment of the presently disclosed circular stapling instrumentincluding independently actuated staple forming and tissue cuttingoperations will now be described in detail with reference to thedrawings wherein like numerals designate identical or correspondingelements in each of the several views. As is common in the art, the term“proximal” refers to that part or component closer to the user oroperator, i.e. surgeon or physician, while the term “distal” refers tothat part or component further away from the user.

FIG. 1 illustrates an embodiment of a circular stapling instrumentaccording to the present disclosure, shown generally as circular stapler10. Circular stapler 10 includes a handle assembly 20 and an elongatebody 30 extending distally from handle assembly 20. A tool assembly 100is mounted on a distal end of elongate body 30. Handle assembly 20includes a fixed handle 22 and a moveable handle or trigger 24. Handleassembly 20 also includes an adjustment knob 26 for moving an anvilassembly 105 relative to cartridge assembly 110 of tool assembly 100.The structure and function of handle assembly 20 will only be describedherein to the extent necessary to fully disclose the operation of toolassembly 100. It is envisioned that tool assembly 100 may be modifiedfor use with any actuation assembly, powered or manual, capable of twoindependent actuation strokes. Commonly owned U.S. patent applicationSer. No. 12/946,082, filed Nov. 15, 2010, the content of which isincorporated by reference herein in its entirety, discloses a surgicaldevice having a powered actuator assembly including first and seconddrive members. In addition, it is envisioned that the independentactuation strokes may be completed by the same drive member completingtwo strokes or by two separate drive members.

With reference to FIG. 2, cartridge assembly 110 of tool assembly 100 isoperably mounted to a distal end of elongate body 30 (FIG. 1) ofcircular stapler 10 (FIG. 1). In one embodiment, cartridge assembly 110is removably secured to elongate body 30 such that cartridge assembly110, or a portion thereof, may be replaced and circular stapler 10 maybe reused. In another embodiment, only a portion of cartridge assembly110 is configured to be removed, and subsequently replaced or reloaded.Alternatively, circular stapler 10 may be configured for a single use,i.e., disposable.

With reference to FIGS. 2 and 3, cartridge assembly 110 includes ahousing 120, a pusher assembly 130A, a staple cartridge 150, and a knifeassembly 160A. Housing 120 of cartridge assembly 110 includes an outercylindrical portion 122, an inner cylindrical body 124 and a pluralityof radially extending supports or ribs (not shown) extending between andinterconnecting inner cylindrical portion 124 and outer cylindricalportion 122. Inner cylindrical portion 124 and outer cylindrical portion122 are coaxial and define a recess 123 therebetween configured toreceive a distal portion of pusher assembly 130A and knife assembly160A.

With continued reference to FIGS. 2 and 3, a proximal end 122 a of outercylindrical portion 122 of housing 120 includes a plurality of tabs 125formed thereon configured to operably engage cartridge assembly 110 witha distal end of elongate body 30 (FIG. 1). Distal end 122 b of outercylindrical portion 122 of housing 120 forms a plurality of tabs 127 bformed therein configured to be received within notches 154 formed instaple cartridge 150. Distal end 122 b of outer cylindrical portion 122of housing 120 also defines a slot 127 a configured to receive aprojection (not shown) formed on staple cartridge 150. Slot 127 a ispositioned such that when the projection is received in slot 127 a, tabs127 b formed on outer cylindrical portion 122 of housing 120 areproperly aligned with notches 154 formed in staple cartridge 150. Outercylindrical portion 122 of housing 120 further defines a plurality ofopenings 129. As will be discussed in further detail below, each of theplurality of openings 129 is configured to engage a pair of a pluralityof detents 138 a, 138 b formed on a distal portion 134 of pusher adapter130.

With reference now to FIG. 3, pusher assembly 130A includes a pusheradapter 130 and a pusher 140. Pusher adapter 130 is a substantiallycylindrical member having a proximal portion 132 and a distal portion134. Proximal portion 132 of pusher adapter 130 is configured foroperable engagement with a drive member (not shown). Distal portion 134of pusher adapter 130 is configured to operably engage pusher 140. Aswill be discussed in further detail below, pusher 140 is not securelyaffixed to pusher adapter 130 such that pusher 140 remains in anadvanced position during the retraction of pusher adapter 130 followingthe first or stapling stroke of circular stapler 10. In this manner, theforce required to move pusher adapter 130 during the second or tissuecutting stroke of circular stapler 10 does not include the forcenecessary to move pusher 140.

With continued reference to FIG. 3, pusher adapter 130 defines alongitudinal passage 131 extending therethrough. A distal end oflongitudinal passage 131 is sized and configured to receive knifeassembly 160A in a sliding manner. Pusher adapter 130 further defines aplurality of longitudinal slots 133 extending along a length thereof.Slots 133 correspond in size and location to the supports (not shown)formed between and interconnecting outer and inner cylindrical portions122, 124 in housing 120. Pusher adapter 130 is configured to be receivedwithin outer cylindrical portion 122 of housing 120 and about innercylindrical portion 124 of housing 120. In this manner, slots 133receive the respective supports (not shown) of housing 120 such thatinner cylindrical portion 124 of housing 120 may be received withinlongitudinal passage 131 of pusher adapter 130. Pusher adapter 130defines a notch 135 on a distal end thereof which creates a distalfacing ledge 136 extending about an inner surface thereof. As will bediscussed in further detail below, notch 135 is configured to receive anouter annular portion of a snap ring 180 of knife assembly 160A and aledge 136 is configured to engage the outer annular portion of snap ring180 during the second or cutting stroke of circular stapler 10. Aplurality of recesses 135 a are formed in a distal surface 134 a ofpusher adapter 130 and are configured to engage tabs (not shown) formedon a proximal facing surface of pusher 140. A plurality of radiallyinwardly extending tabs 136 a is spaced distal of ledge 136. As will bediscussed in further detail below, tabs 136 a are configured to retainsnap ring 180 in engagement within a distal end of pusher adapter 130.As discussed above, pusher adapter 130 includes a plurality of paireddetents 138 a, 138 b configured to be selectively received withinopenings 129 formed in outer cylindrical portion 122 of housing 120.

With reference still to FIG. 3, pusher 140 includes a proximal portion142 and a distal portion 144. Proximal portion 142 of pusher 140 definesa plurality of tabs (not shown) configured to be selectively receivedwithin the plurality of recesses 135 a formed on distal surface 134 a ofpusher adapter 130.

As will also be discussed in further detail below, at the completion ofthe second or cutting stroke of circular stapler 10 pusher assembly 130Ais completely retracted relative to housing 120. In the completelyretracted position, pusher 140 is disengaged from pusher adapter 130. Inthis manner, pusher 140 and staple cartridge 150 may be separated fromhousing 120.

With continued reference to FIG. 3, distal portion 144 of pusher 140includes a plurality of pusher members 146 extending distally therefromand arranged in three concentric rows. Pusher members 146 align withstaples “S” received within staple cartridge 150 such that advancementof pusher 140 relative to staple cartridge 150 causes ejection ofstaples “S” from staple cartridge 150.

With reference to FIGS. 2 and 3, staple cartridge 150 is a substantiallycylindrical member configured to operably engage distal end 122 b ofouter cylindrical portion 122 of housing 120 and defines a longitudinalopening 151 configured to receive knife 170 of knife assembly 160Atherethrough. Staple cartridge 150 includes a plurality of staplereceiving pockets 152 disposed about opening 151 arranged in threeconcentric rows. Staple receiving pockets 152 align with pusher members146 formed on distal portion 144 of pusher 140. As discussed above,staple cartridge 150 also includes a plurality of notches 154 and aprotrusion (not shown). Notches 154 are configured to operably engagedistal portion 122 b of outer cylindrical portion 122 of housing 120 andthe protrusion (not shown) of staple cartridge 150 is configured to bereceived in slot 127 a of outer cylindrical portion 122 to assure theproper alignment of staple cartridge 150 with outer cylindrical portion122 of housing 120.

With reference now to FIGS. 3-7, knife assembly 160A includes a knifecarrier 160, a circular knife 170, and a snap ring 180. With particularreference to FIG. 5, knife carrier 160 is a substantially cylindricalmember having a proximal portion 162, a distal portion 166 and anannular ridge 164 formed therebetween. Knife carrier 160 is configuredto be longitudinally translatable through longitudinal passageway 131 ofpusher adapter 130. Knife carrier 160 defines a longitudinal passage 161extending therethrough. Proximal portion 162 of knife carrier 160defines an annular groove 163 configured to accommodate snap ring 180when snap ring 180 is in either a first or compressed condition or in asecond or expanded condition. As will be discussed in further detailbelow, when circular stapler 10 is in the first or initial position, andprior to retraction of pusher adapter 130 following the first stroke ofcircular stapler 10, snap ring 180 is received completely within annulargroove 163 formed in knife carrier 160. Proximal portion 162 of knifecarrier 160 further defines a step 162 a formed in annular groove 163.As will be discussed in further detail below, step 162 a is configuredto engage an inner annular portion of snap ring 180 when snap ring 180is in the second or expanded condition. As will also be discussed infurther detail below, engagement of snap ring 180 with step 162 aprevents radial compression of snap ring 180 during the second or tissuecutting stroke.

With continued reference to FIGS. 5 and 6, annular ridge 164 extendsradially outward from between proximal and distal portions 162, 166 ofknife carrier 160. Annular ridge 164 is configured to engage a proximalend of snap ring 180. Distal portion 166 of knife carrier 160 isconfigured to receive snap ring 180 and circular knife 170 thereabout.In particular, as seen in FIGS. 3 and 5, distal portion 166 defines apair of opposed recesses 167 configured to engage respective lockingtabs 176 formed on knife 170.

With particular reference still to FIG. 5, knife 170 is a substantiallycylindrical member having proximal and distal ends 172, 174 and defininga longitudinal opening 171 extending therethrough. Knife 170 is sizedand configured to be received through longitudinal opening 141 of staplecartridge 140. Distal end 174 of knife 170 includes a sharpened surface174 a defining a knife edge configured for cutting tissue. As discussedabove, proximal end 172 of knife 170 is configured to be received aboutdistal portion 166 of knife carrier 160 and includes a pair of opposedtabs 176 configured to be received within respective recesses 167 formedin distal portion 166 of knife carrier 160.

With reference to FIGS. 5-7, snap ring 180 is a substantially C-shapedmember having a substantially rectangular transverse cross-sectionalprofile and defining a central passage 181 therethrough. Snap ring 180includes a first diameter “d₁” when in the first or radially compressedcondition (FIG. 8) and a second diameter “d₂” when in the second oruncompressed condition (FIG. 10).

When in the first or radially compressed condition, snap ring 180 issized to be substantially entirely received within annular groove 163formed in proximal portion 162 of knife carrier 160. As such, when inthe radially compressed condition, no portion of snap ring 180 extendsbeyond an outer diameter of knife carrier 160, thereby permittingrelative movement between pusher adapter 130 and knife carrier 160.

When in the second or uncompressed condition, snap ring 180 is sized tosimultaneously engage pusher adapter 130 and knife carrier 160. Inparticular, an outer annular portion of snap ring 180 is configured toengage ledge 136 created in the distal end of pusher adapter 130 bynotch 135 and an inner annular portion of snap ring 180 is configured toengage knife carrier 160 adjacent step 162 a formed therein. As notedabove, and as will be discussed in further detail below, step 162 aformed in knife carrier 160 prevents radial compression of snap ring 180during the second or tissue stapling stroke of circular stapler 10.

The operation of cartridge assembly 110 will now be described withreference to FIGS. 8-12. Referring initially to FIG. 8, cartridgeassembly 110 is shown in a first or initial condition. In the initialcondition, pusher assembly 130A is received between outer and innercylindrical portions 122, 124 of housing 120. Knife assembly 160A isreceived within longitudinal passage 131 of pusher adapter 130 and aboutinner cylindrical portion 124 of housing 120. Staple cartridge 150 is inoperative engagement with distal end 120 b of housing 120 to operablyretain pusher assembly 130A and knife assembly 160A within housing 120.Snap ring 180 is in the first or radially compressed condition andreceived within annular groove 163 formed on knife carrier 160. Snapring 180 is maintained in the radially compressed condition by an innerwall of pusher adapter 130. Notch 135 formed in the distal end of pusheradapter 130 is disposed distal of annular groove 163 and snap ring 180.In this manner, pusher assembly 130A may be advanced distally withoutcausing the advancement of knife assembly 160A.

In the initial position, pusher assembly 130A is prevented frominadvertent distal advancement relative to housing 120 throughengagement of the plurality of paired detents 138 a, 138 b (FIG. 3)formed on distal portion 134 of pusher adapter 130 with openings 129(FIG. 2) formed in outer cylindrical portion 122 of housing 120.

With reference now to FIG. 9, during a first or staple forming stroke ofcircular stapler 10 (FIG. 1), following approximation of anvil assembly105 against cartridge assembly 110, retraction or actuation of trigger24 (FIG. 1) relative to handle 22 (FIG. 1) causes advancement of a driveassembly (not shown) which operably engages pusher adapter 130 to causethe advancement of pusher assembly 130A, as indicated by arrows “A”.Advancement of pusher adapter 130 advances pusher 140 thereby causingpusher members 146 on distal portion 144 thereof to be advanced intoand/or through staple receiving pockets 152 of staple cartridge 150 andto eject staples “S” from staple cartridge 150. Although not show, theejection of staples “S” (FIG. 3) from staple cartridge 150 causesadvancement of staples “S” against an anvil 106 of anvil assembly 105.Anvil 106 defines a plurality of recesses or forming pockets (not shown)corresponding in number and location to pockets 152, and being shaped toform staples “S”. Forming of staples “S” secures the tissue retainedbetween staple cartridge 150 and anvil assembly 105.

During the stapling stroke, knife assembly 160A may be maintained orheld in place relative to housing 120 through engagement of one or moreprotrusions (not shown) formed on an inner surface of knife carrier 160and/or on an outer surface of inner cylindrical portion 124 of housing120 with one or more corresponding detents (not shown) formed on theother of the outer surface of inner cylindrical portion 124 and theinner surface of knife carrier 160.

With reference to FIG. 10, upon completion of the stapling stroke,pusher adapter 130 is retracted proximally relative to housing 120, asindicated by arrows “B”, to a position proximal of its initial position(FIG. 8) prior to the staple forming stroke. Pusher 130 is sufficientlyretracted relative to knife carrier 160 and snap ring 180 such that snapring 180 is aligned with notch 135 formed in the distal end of pusheradapter 130. Alignment of notch 135 with snap ring 180 allows snap ring180 to move from the first or compressed condition (FIG. 8) to theuncompressed condition, i.e., snap ring 180 is able to decompress orradially expand.

With reference now to FIG. 11, during the second or cutting stroke ofcircular stapler 10 (FIG. 1), a second retraction or actuation oftrigger 24 (FIG. 1) relative to handle 26 (FIG. 1) causes advancement ofthe drive member (not shown) which operably engages pusher adapter 130to cause the advancement of pusher adapter 130, as indicated by arrows“C”. Advancement of pusher adapter 130 causes ledge 136, defined bynotch 135 formed in the distal end of pusher adapter 130, to engage anouter portion of snap ring 180 while an inner portion of snap ring 180remains engaged with knife carrier 160. In particular, step 162 a,formed within groove 163 of knife carrier 160, engages snap ring 180 andprevents snap ring 180 from being radially compressed back into annulargroove 163 during the second advancement of pusher adapter 130 duringthe second or tissue cutting stroke of circular stapler 10. Accordingly,step 162 a of knife carrier 160 maintains snap ring 180 in the second orexpanded condition such that snap ring 180 remains in contact with bothpusher adapter 130 and knife carrier 160 to assure the simultaneousadvancement of knife assembly 160A with the advancement of pusheradapter 130, as indicated by arrows “C”.

Turning to FIG. 12, continued advancement of pusher adapter 130 causesknife 170 to be received through longitudinal opening 151 of staplecartridge 150, thereby severing the tissue retained between staplecartridge 150 and anvil assembly 105. It is envisioned that pusherassembly 130A and knife assembly 160A may be configured such thatretraction of the drive assembly (not shown) causes the retraction ofpusher adapter 130 and pusher 140 of pusher assembly 130A, and knifecarrier 160, knife 170 and snap ring 180 of knife assembly 160A.

The use of circular stapler 10 will now be described with reference tothe figures, namely FIGS. 1 and 8-12. In use, circular stapler 10 isoperated in a manner substantially similar to a traditional circularstapler. Once oriented such that the tissue to be stapled is receivedbetween cartridge assembly 110 and anvil assembly 105 and anvil assembly105 is approximated towards cartridge assembly 110, trigger 24 may besqueezed to cause the actuation of handle assembly 20. As discussedabove, actuation of handle assembly 20 causes a first advancement of adrive assembly (not shown) which engages and causes the advancement ofpusher assembly 130A. During the first or staple forming stroke, pusherassembly 130A is moved relative to housing 120 and knife assembly 160Awhile knife assembly 160A remains stationary relative to housing 120. Inthis manner, during the first or staple forming stroke of circularstapler 10 only the staple forming function is performed. Accordingly,the force required for completion of the first stroke of circularstapler 10 does not include the force necessary to also cut the tissuesimultaneously therewith.

Upon completion of the first or staple forming stroke, trigger 24(FIG. 1) is released to permit the retraction of the drive member (notshown) and pusher adapter 130 of pusher assembly 130A. As discussedabove, pusher adapter 130 is retracted to a position proximal of itsinitial position. In one embodiment, pusher adapter 130 is retracted0.25 inches further back from its initial starting position. In thisretracted position, notch 135 formed in the distal end of pusher adapter130 is aligned with snap ring 180 thereby allowing snap ring 180 toexpand from the first or compressed condition (FIG. 8) to the second oruncompressed condition (FIG. 10).

A subsequent squeezing or actuation of trigger 24 causes a secondadvancement of the drive member and pusher adapter 130. Advancement ofpusher adapter 130 causes engagement of ledge 136 of pusher adapter 130with snap ring 180. Since snap ring 180 remains engaged with knifecarrier 160 in addition to engagement with pusher adapter 130,advancement of pusher adapter 130 causes the advancement of knifeassembly 160A. Advancement of circular knife 170 of knife assembly 160Acauses the cutting of tissue positioned between cartridge assembly 110and anvil assembly 105. Because staples “S” were ejected and formedduring the first stroke of circular stapler 10, and pusher 140 remainedin the advanced position (FIG. 9) upon retraction of pusher adapter 130following the first or staple forming stroke, the force required tocomplete the second or cutting stroke of circular stapler 10 is lessthen the force that would be necessary to complete both the stapleejecting/forming and tissue cutting procedure. It is envisioned that theforce provided by the drive member during the second stroke would besufficient to disengage any securing mechanism maintaining knifeassembly 160A relative to inner cylindrical housing 124 of housing 120.As discussed above, the securing mechanism may include protrusions (notshown) formed on the inner surface of knife carrier 160 and/or on theouter surface of inner cylindrical portion 124 of housing 120 configuredto be received within detents (not shown) formed on the other of theouter surface of inner cylindrical portion 124 and/or on the innersurface of knife carrier 160 such that knife assembly 160A is permittedto advance distally relative to housing 120.

Upon completion of the tissue cutting stroke, pusher adapter 130 isretracted proximally to one of the initial position (FIG. 8) or theretracted position (FIG. 11). As discussed above, pusher assembly 130Aand knife assembly 160A may be configured such that either or both ofpusher assembly 130A and knife assembly 160A are retracted following thesecond or cutting stroke of circular stapler 10 (FIG. 1). Refraction ofpusher adapter 130 to one of the initial or retracted positions causesdisengagement of pusher 140 from pusher adapter 130. In this manner,pusher 140 and empty staple cartridge 150 may be separated or unloadedfrom housing 120 and replaced with a new pusher 140 and staple cartridge150.

In addition to the reduced force requirements provided by the two strokeoperation of circular stapler 10, the independent or decoupled stapleforming and tissue cutting function of circular stapler 10 also permitsthe varying of the staple crimp height relative to the knife traveldistance, the varying of the staple travel speed relative to the knifetravel speed, and/or the addition of a dwell time between stapleformation and tissue cutting. This configuration allows a clinician tooptimize staple crimp heights to given conditions, such as, tissuethickness, tissue compliance and clamping force. This configuration mayalso allow for the monitoring of staple forming and knife cuttingforces, to alert the clinician in case an abnormal force is detected.This configuration further allows force and other data to be monitoredand used for data collection and research, which when analyzed, may leadto further optimization of operational parameters, such as staple crimpheight and dwell and travel speed. By independently controlling andoptimizing these various parameters, improved hemostasis and anastomonicjoint strength may result across a much broader range of tissuethicknesses, thereby allowing a clinician to have improved andcustomized control over the results. Further still, when the staplingand cutting functions are performed at the same time, the tissue beingstapled may be displaced by the knife, thereby causing the staple legsto deflect and misalign with their intended anvil pockets, resulting inpoor staple formation and possible leakage.

It will be understood that various modifications may be made to theembodiment disclosed herein. For example, circular stapler 10 mayinclude a mechanism for changing cartridge assembly 110 from two strokeoperation to a single stroke operation. Therefore, the above descriptionshould not be construed as limiting, but merely as exemplifications ofparticular embodiments. Those skilled in the art will envision othermodifications within the scope and spirit of the claims appended hereto.

The invention claimed is:
 1. A circular stapler comprising: a handleassembly; an elongate body extending from the handle assembly; and, acartridge assembly mounted on a distal end of the elongate body, thecartridge assembly including a pusher assembly, a knife assemblyreceived within the pusher assembly, and a compression member disposedbetween the pusher assembly and the knife assembly and movable between acompressed condition and an expanded condition, wherein the knifeassembly is selectively fixed relative to the pusher assembly by thecompression member for independent movement of the pusher assemblyrelative to the knife assembly, the knife assembly being initiallydetached from the pusher assembly during a first stroke of the handleassembly when the compression member is in the compressed condition, andsubsequently attached to the pusher assembly during a second stroke ofthe handle assembly when the compression member is in the expandedcondition, wherein the knife pusher is configured to maintain thecompression member in the expanded condition during the second stroke.2. The circular stapler of claim 1, wherein the pusher assembly includesa pusher adapter configured to be advanced a first distance andretracted a second distance, the second distance being greater than thefirst distance.
 3. The circular stapler of claim 2, wherein thecompression member includes a snap ring, the knife assembly supportingthe snap ring therearound, the pusher adapter includes a ridge formedabout an inner surface thereof configured to engage the snap ring. 4.The circular stapler of claim 3, wherein the knife assembly includes aknife carrier, and a knife supported on and extending distally from theknife carrier.
 5. The circular stapler of claim 4, wherein the knifecarrier includes an annular groove configured to accommodate the snapring when the snap ring is in a radially compressed condition and whenthe snap ring is in an uncompressed condition.
 6. The circular staplerof claim 5, wherein the snap ring extends beyond an outer diameter ofthe knife carrier when the snap ring is in the uncompressed condition.7. The circular stapler of claim 5, wherein the knife carrier furtherincludes a step formed in the annular groove configured to engage thesnap ring when the snap ring is in the uncompressed condition.
 8. Thecircular stapler of claim 7, wherein the step is configured to preventradial compression of the snap ring during a tissue cutting stroke. 9.The circular stapler of claim 4, wherein the snap ring is maintainedwithin an outer diameter of the knife carrier when the snap ring is inthe compressed condition.
 10. The circular stapler of claim 1, whereinthe cartridge assembly includes a housing having an outer cylindricalportion and an inner cylindrical portion, wherein the pusher assemblyand knife assembly are substantially cylindrical and are selectivelyreceived between the inner and outer cylindrical portions of thehousing.
 11. A cartridge assembly for a circular stapler, the cartridgeassembly comprising: a shell; a pusher assembly movably disposed withinthe shell; a knife assembly received within the pusher assembly; and acompression member supported between the pusher assembly and the knifeassembly, the compression member being movable between a compressedcondition in which the pusher the pusher assembly and the knife assemblyare independently movable to an expanded condition in which the pusherassembly and the knife assembly are connected by the compression memberand movable in unison, wherein the knife assembly is configured toprevent the compression member from moving from the expanded conditionback to the compressed condition.
 12. The circular stapler of claim 11,wherein the compression member includes a snap ring, the knife assemblysupporting the snap ring therearound, the pusher adapter includes aridge formed about an inner surface thereof configured to engage thesnap ring.
 13. The circular stapler of claim 12, wherein the knifeassembly includes a knife carrier, and a knife supported on andextending distally from the knife carrier.
 14. The circular stapler ofclaim 13, wherein the knife carrier includes an annular grooveconfigured to accommodate the snap ring when the snap ring is in aradially compressed condition and when the snap ring is in anuncompressed condition.
 15. The circular stapler of claim 14, whereinthe snap ring is maintained within an outer diameter of the knifecarrier when the snap ring is in the compressed condition.
 16. Thecircular stapler of claim 15, wherein the snap ring extends beyond anouter diameter of the knife carrier when the snap ring is in theuncompressed condition.
 17. The circular stapler of claim 16, whereinthe knife carrier further includes a step formed in the annular grooveconfigured to engage the snap ring when the snap ring is in theuncompressed condition.
 18. The circular stapler of claim 17, whereinthe step is configured to prevent radial compression of the snap ringduring a tissue cutting stroke.
 19. The circular stapler of claim 11,wherein the cartridge assembly includes a housing having an outercylindrical portion and an inner cylindrical portion, wherein the pusherassembly and knife assembly are substantially cylindrical and areselectively received between the inner and outer cylindrical portions ofthe housing.